You found the temperature sensitivity of Li-Ion batteries. The perform optimally at room temperature. When they get too hot or too cold they lose a lot of their charge capacity. When they're warm straight off the charger they will not run as long as when they've cooled completely. However, when Li-Ion batteries get too cold, they can lose a majority of their run time. The narrow temperature tolerance of Li-Ion batteries keeps them out of use for some applications.
Li-Ion chargers follow a very strict charging profile. They don't trickle charge, that's a Li-Ion battery no-no. There are two primary phases for Li-Ion charging than that's CCM and CVM. In CVM current falls off as voltage approaches terminal charging voltage, but that's not to be confused with trickle charging. That's just the latter phase of a normal Li-Ion charging profile.
On the other hand, Lead-Acid batteries and NiCad or NiMH batteries rely on trickle charging to keep the charge topped off and maximize battery longevity. Those types of batteries "self-discharge". Li-Ion batteries do not self-discharge and do require any kind of trickle charging. Doing that puts additional wear on them with no benefit.
The standard tolerance on terminal charging voltage for 4.2V Li-Ions is 4.25V. As you increase that terminal voltage, you increase wear. If a battery is coming off the charger at 4.3 Volts, I'd bin the charger. Of course, you have to make sure the accuracy of your voltmeter is good for that amount. Cheapo meters you get on eBay or at discount tool stores can have quite a bit of error.